Merge branch '4.4' into 5.4

* 4.4:
  [HttpKernel] lock when writting profiles
  Using identical comparison for path validation
  [Mime] Fix email rendering when having inlined parts that are not related to the content
  [HttpFoundation] move flushing outside of Response::closeOutputBuffers
  [FrameworkBundle] Do not throw when describing a factory definition
  Fix checking result of DateTime::getLastErrors

Author: nicolas-grekas

Extension/Core/DataTransformer/DateTimeToStringTransformer.php

@@ -121,7 +121,7 @@ public function reverseTransform($value)
         $outputTz = new \DateTimeZone($this->outputTimezone);
         $dateTime = \DateTime::createFromFormat($this->parseFormat, $value, $outputTz);
 
-        $lastErrors = \DateTime::getLastErrors();
+        $lastErrors = \DateTime::getLastErrors() ?: ['error_count' => 0, 'warning_count' => 0];
 
         if (0 < $lastErrors['warning_count'] || 0 < $lastErrors['error_count']) {
             throw new TransformationFailedException(implode(', ', array_merge(array_values($lastErrors['warnings']), array_values($lastErrors['errors']))));